1. Field of the Invention
The present invention relates to a semiconductor device for controlling a battery to be charged with a sine curve charger, and to a rechargeable power supply unit to be charged with a sine curve charger.
2. Description of the Related Art
In recent years, portable electronic devices have been widely used. The electronic devices operate using a battery. In a case where the battery does not operate normally, a user cannot use the electronic device at a destination or an unexpected accident may occur in some cases. Accordingly, charge and discharge of the battery is monitored (for example, see JP 2001-178011 A).
During the charge of the battery, when a voltage of the battery becomes equal to or higher than an overcharge detection voltage which is used in a case of detecting an overcharge state, after the elapse of an overcharge determination time necessary for determining the overcharge state, the overcharge state of the battery is determined and the charge of the battery is inhibited.
During the discharge of the battery, when the voltage of the battery becomes lower than an overdischarge detection voltage which is used in a case of detecting an overdischarge state, after the elapse of an overdischarge determination time necessary for determining the overdischarge state, the overdischarge state of the battery is determined and the discharge of the battery is inhibited. After that, operation of part of circuits provided in are chargeable power supply unit is stopped, which results in lowering power consumption of the rechargeable power supply unit. Such a state is referred to as a power-down state. The rechargeable power supply unit has a VM terminal for monitoring whether or not the state of the rechargeable power supply unit is to be shifted to the power-down state. When a voltage at the VM terminal becomes equal to or higher than a power-down voltage, the state of the rechargeable power supply unit shifts to the power-down state. When the voltage at the VM terminal becomes lower than the power-down voltage, the power-down state of the rechargeable power supply unit is cancelled.
Further, when a charger is connected to the battery in the power-down state, the power-down state is cancelled, to thereby start the charge of the battery. When the voltage of the battery becomes equal to or higher than the overdischarge detection voltage, after the elapse of a delay time for cancellation of the overdischarge state, which is necessary for determining the cancellation of the overdischarge state, a normal state of the battery is determined. When the battery is further charged, the voltage of the battery becomes equal to or higher than the overcharge detection voltage. Then, after the elapse of the overcharge determination time, the overcharge state of the battery is determined.
In this case, it is assumed that the charger for charging the battery is a sine wave charger and the delay time for cancellation of the overdischarge state is longer than a ½ cycle of a charging voltage of the sine wave charger. At this time, in a case where the state of the rechargeable power supply unit has been shifted to the power-down state and the battery is charged with the sine wave charger, even when the voltage of the battery exceeds the overdischarge detection voltage, a time period during which the voltage of the battery exceeds the overdischarge detection voltage is shorter than the delay time for cancellation of the overdischarge state. As a result, the delay time for cancellation of the overdischarge state never elapses. Accordingly, the overdischarge state of the battery is not cancelled, and the overcharge state is not detected even in a case where the charge cannot be stopped. Note that, in this case, shift and cancellation of the power-down state are repeated as shown in FIG. 3.